Image data comprises a number of pixels having a number of components that contribute to defining the image, such as color, chroma, hue, brightness, and/or intensity. Each pixel of the image is assigned a number or a set of numbers representing the magnitude of color at that particular spot. Binary image data has two possible values for each pixel, black (or a specific color) (represented by the number “1”) or white (represented by the number “0”). Images that have a large range of shades are referred to as grayscale images. For example, grayscale images have an 8-bit value per pixel comprising 256 tones or shades of gray for each pixel in the image (gray level of 0 to 255). Grayscale image data may also be referred to as continuous tone or contone image data. For color images, grayscale refers to shades of color. The pixels in a color image may be defined in terms of a color space, typically with three values, such as RGB—R for red, G for green, and B for blue—or four values, such as CMYK—C for cyan, M for magenta, Y for yellow, and K for black, although any range of values can be used.
The pixels may also be defined in terms of device independent space (e.g., when inputting image data, such as standard RGB (sRGB) or CIE L*a*b) or a device dependent space (e.g., when outputting image data, such as device RGB or device CMYK). When outputting image data to an output device (e.g., copier, printer, or multi-function device (MFD)), a fraction of the maximum possible marked density may be used to identify how much ink is employed for a print or copy job. Such information may typically be used for billing a user for print or copy jobs. For example, some methods employ a billing strategy based on an estimated amount of ink or toner consumption; others bill users based on a print mode selection (e.g., draft, standard, color, enhanced, etc.) of the output device. In dynamic print-job environments, because printing documents using black ink or toner is less expensive than using colored ink or toner, billing is often based on the amount of color content contained in the job to be printed. In order to bill users for color printing, color detection is an important feature required in an image path. Color detection is used to analyze documents for presence of color as well as an amount of color in order to bill users accordingly. Generally, the higher the presence and amount of color in a document, the higher the cost.
Some systems include counting the number of pixels in the image data of the document to be printed. For example, a number of binary pixels associated with the CMYK color planes may be counted to determine a pixel count for each category of color at the time of marking for output in the image path. Generally, with existing color detection and counting methods, a pixel will be labeled as color when the presence of any one of the C, M, and Y signals is detected. U.S. patent application Ser. No. 12/252,391 (published as Patent Application No. 2010/0100505 A1), filed Oct. 16, 2008 by the same Assignee (Xerox Corporation), which is hereby incorporated by reference in its entirety, proposes a way to count color pixels. In solid ink and ink jet products, however, it is desirable to render neutral gray objects with CMYK ink (e.g., create objects that appear gray to the human eye by using a particular combination of C, M, Y, and K, thus enabling higher image quality. This combination of C, M, Y, and K is referred to as process color, rich black, or composite black. For billing purposes, users do not desire to be charged for color pixels that were (are) supposed to be gray (neutral with respect to color; a shade of black (not as in grayscale)). The above-referenced '505 publication, for example, has limitations in handling images that are converted to contone from rendered binary data. Moreover, the '505 publication inhibits counting of gray pixels that are converted to process color by system electronics as being counted as color pixels.
In a typical multi-tier billing system for production printers, images are placed into different tiers based on the amount of color content on each page. Placing the image in the correct tier level is important both from the user's, as well as the company's, perspective. Solid ink jet printer machines render neutral areas of an image with a combination of cyan, magenta, yellow, black (CMYK) toner/ink when printing or copying. This, however, creates problems in billing since these “gray” counts may be composed of color toners that mimic gray but are counted towards color.
This is because most existing billing systems are based on counting the number of color pixels in the C, M, Y planes. Use of process (or “rich”) black to render monochrome content makes it difficult to implement a multi-tier billing scheme based on use of color that is both reliable and fair in the user's eyes. For instance, a given pixel may be counted as a color pixel when the presence of any one of the C, M, and Y signals is detected—although it may actually be neutral gray. This increases the possibility of a page with composite black or gray to be classified as color, which is undesirable, because the color content results used to determine a billing strategy for a document (or image) may be skewed. Superior monochrome image quality that is delivered by use of process neutrals could be billed as neutral; however, an unsophisticated user may not differentiate this from very dark colored areas that should be billed as color. A per-ink pixel counting based algorithm measures by quantity and applies an imperfect mapping algorithm in an attempt to infer color content. As a result, at times the user will pay the color price for a neutral page, and at times the user will charged a monochrome price for a color page. This leads either to lost revenue or users that perceive that they have been overcharged.
Accordingly, an improved system and method of categorizing color content according to the quantity and types of color used as well as its perception by the human eye, enabling billing paradigms that are better correlated to the value received by the user is desirable.